Engagement is often seen as the holy grail of online video measurement, but brands shouldn't neglect reach and GRP either, says James Kiernan, senior VP and managing director at ZenithOptimedia, in this interview with Beet.TV.

Reach and GRP are valuable because they can be looked at as common metrics to compare success of online video against TV, he said. That's particularly helpful as agencies and brands look to move more money into online video. Engagement is certainly useful though, as it often provides insight into a consumer's willingness to buy a product or service, Kiernan added. He also said that earned media works best when paid media can be used first as a catalyst.

Kiernan was a participant in Tuesday's Beet.TV Summit on Video Engagement. We spoke with him before the session.

Daisy Whitney